1. Field of the Invention
This invention relates to methods for removing solvent-insoluble tives of para-xylylene from predetermined, desired areas of substrates carrying such coatings, and to compositions for use in such methods.
2. Discussion of Background Art
In the fabrication of electronics assemblies such as printed circuit boards and ceramic circuit boards, a popular and frequently used coating for the circuit boards, for components on the boards, and for connectors and leads linking elements on the boards to one another and to devices not directly attached to the boards has been vacuum vapor-phase-deposited, polymerized paraxylylene and vacuum vapor-phase-deposited, polymerized substituted derivatives of para-xylylene such as poly-para-xylylene itself, sometimes called parylene N, poly-monochloro-para-xylylene, commonly called parylene C, and poly-dichloro-para-xylylene, commonly called parylene D. These parylenes, and particularly parylene C, are among the best conformal coatings for electronics, for they impart good water impermeability, high resistance to solvents, high resistance to heat, and excellent coefficients of thermal expansion. Moreover, they are normally deposited in such thin layers that the electrical properties of electronic devices are unaffected by their presence. However, these coatings are exceedingly difficult to remove, for most parylenes are insoluble in common solvents.
Efforts to abrade parylene coatings from electronics components, printed circuit boards and flex harnesses have proved ineffective. Abrasion tends to damage the coated electronic assemblies and adjacent parts, generates dirt and dust that are difficult to remove, and is difficult to confine to a precise area where the coating is desired to be removed without affecting contiguous coating areas. Other methods of removing parylene, such as plasma etching, are time consuming, costly, and often result in broken or damaged components and substrates.
For some time, a need has existed for a simple, cost-effective method, suitable for field use, for removing parylene coatings from substrates, particularly substrates such as printed wiring boards, ceramic circuit boards, and electronic circuits that are densely packed with parylene-coated components and leads. Such methods must remove the coatings from desired, predetermined areas without affecting contiguous or adjacent components whether coated or uncoated.